An immunosuppressive substance termed early pregnancy factor (EPF) has been detected in the maternal circulation within hours after fertilisation. It has been implicated in a maintenance role with respect to the allogeneic foetus during pregnancy. However, the rosette inhibition test, which is used for the measurement of EPF activity, is a technically difficult and time consuming assay, such that some laboratories fail to regularly detect the molecule in pregnancy serum. Thus EPF measurement and investigation has become a controversial topic. We therefore propose to (1) develop a more clinically applicable alternative methodology; (2) study the physical, immunochemical and biological characteristics of the molecule; and (3) provide a model for the mechanism of action of EPF. We also plan to generate a monoclonal antibody to EPF by the hybridoma technique. Such an antibody would facilitate (1) the isolation of purified material which may have important clinical applications, (2) the localization of EPF distribution in tissues within the body and the site of production of EPF. Finally, we plan to establish ourselves as a reference centre for the study of EPF by providing purified material and standards to other laboratories. This will further the investigation of this potentially important substance and achieve some degree of correlation between laboratories. Both human and mouse EPF will be studied. We will use the rosette-inhibition test initially to detect EPF and then will develop a faster and less cumbersome assay based on the known affinity of EPF for cell surfaces and also on the ability of EPF to inhibit complement activation. Using these two assays we will then develop a monoclonal antibody against EPF. Human EPF will be isolated by gel-filtration and ion-exchange chromatography and its molecular weight, subunit components, if any, proportions of carbohydrate and amino acids, isoelectric point, solubility and biological activity will be determined. Particular emphasis will be placed on the ability of EPF to bind to lymphocytes and to interfere with complement dependent cytolytic reactions. In summary this project aims at defining the properties of one of the potentially most exciting pregnancy-associated molecules discovered in recent years.